Image projection apparatus and image projection method

Abstract

An image projection method includes: reflecting, by a concave mirror, light having transmitted through one or more lenses after forming an intermediate-focused image of the light; and projecting an image onto a projection plane through reflecting the light reflected by the concave mirror by a plane mirror that has an aspect ratio of 1.9 or more.

The invention is claimed as follows: 
     
       1. An image projection apparatus, comprising:
 a projection optical system including one or more lenses, a concave mirror, and a plane mirror that are provided in order from a light incidence side on which incident light is incident, and configured to project an image using the incident light, 
 wherein the one or more lenses are configured to form an intermediate-focused image on a near side of the concave mirror, and the plane mirror has an aspect ratio of 1.9 or more; and 
 a transparent flat plate on an optical path connecting the concave mirror and the plane mirror, 
 wherein the one or more lenses configure a symmetric optical system disposed on an optical axis, and 
 wherein a distance, at which each of a passing beam centroid position on the light incidence side of the transparent flat plate and a passing beam centroid position on a light emission side of the transparent flat plate are disposed from the optical axis of the one or more lenses, is based on a focal distance of the projection optical system. 
 
     
     
       2. The image projection apparatus according to  claim 1 , wherein
 the distance is 4.6 times or less as long as the focal distance of the projection optical system. 
 
     
     
       3. The image projection apparatus according to  claim 1 , wherein a distance between a beam centroid position of the plane mirror and the optical axis of the one or more lenses is 1.42 times or more as large as a curvature radius of the concave mirror. 
     
     
       4. The image projection apparatus according to  claim 1 , wherein a distance between the transparent flat plate and the optical axis of the one or more lenses is 0.3 times or less as long as another distance between a beam centroid position of the plane mirror and the optical axis of the one or more lenses. 
     
     
       5. The image projection apparatus according to  claim 1 , further comprising an angle adjustment mechanism configured to adjust an angle of the plane mirror. 
     
     
       6. The image projection apparatus according to  claim 1 , further comprising a switching mechanism configured to switch between a first projection mode and a second projection mode while maintaining a posture of the one or more lenses and a posture of the concave mirror, the first projection mode disposing the plane mirror on an optical path, and the second projection mode disposing the plane mirror off the optical path. 
     
     
       7. The image projection apparatus according to  claim 6 , further comprising a housing configured to accommodate the one or more lenses and the concave mirror, wherein, in the first projection mode, light reflected by the plane mirror is projected onto a plane that is along a mounting surface of the housing, and in the second projection mode, light from the concave mirror is projected onto a plane intersecting with the mounting surface of the housing without traveling through the plane mirror. 
     
     
       8. The image projection apparatus according to  claim 6 , wherein the image is projected onto a projection plane that forms an angle of about 45 degrees with respect to the plane mirror. 
     
     
       9. The image projection apparatus according to  claim 1 , further comprising:
 an illumination optical system; and 
 a light modulation device configured to modulate, based on an image signal, illumination light from the illumination optical system. 
 
     
     
       10. An image projection apparatus, comprising:
 a projection optical system including one or more lenses, a concave mirror, and a planar optical substrate that are provided in order from a light incidence side on which incident light is incident, and configured to project an image using the incident light, 
 wherein the one or more lenses are configured to form an intermediate-focused image on a near side of the concave mirror, and the planar optical substrate is configured to reflect a part of the incident light while allowing the other part of the incident light to transmit therethrough; and 
 a transparent flat plate on an optical path connecting the concave mirror and the plane mirror, 
 wherein the one or more lenses configure a symmetric optical system disposed on an optical axis, and 
 wherein a distance, at which each of a passing beam centroid position on the light incidence side of the transparent flat plate and a passing beam centroid position on a light emission side of the transparent flat plate are disposed from the optical axis of the one or more lenses, is based on a focal distance of the projection optical system. 
 
     
     
       11. The image projection apparatus according to  claim 10 , wherein the planar optical substrate is configured to reflect or allow the incident light to transmit therethrough depending on a wavelength of the incident light, or reflect or allow the incident light to transmit therethrough depending on polarization of the incident light. 
     
     
       12. An image projection apparatus, comprising:
 a projection optical system including one or more lenses, a concave mirror, and a plane mirror that are provided in order from a light incidence side on which incident light is incident, and configured to project an image using the incident light; 
 a switching mechanism, 
 wherein the one or more lenses are configured to form an intermediate-focused image on a near side of the concave mirror, and 
 wherein the switching mechanism is configured to switch between a first projection mode and a second projection mode while maintaining a posture of the one or more lenses and a posture of the concave mirror, the first projection mode disposing the plane mirror on an optical path, and the second projection mode disposing the plane mirror off the optical path; and 
 a planar optical substrate configured to reflect a part of the incident light while allowing the other part of the incident light to transmit therethrough, 
 wherein the switching mechanism is configured to switch between a third projection mode and one of the first and second projection modes, the third projection mode disposing the plane mirror off the optical path and disposing the planar optical substrate on the optical path. 
 
     
     
       13. The image projection apparatus according to  claim 12 , further comprising a housing configured to accommodate the one or more lenses and the concave mirror,
 wherein, in the first projection mode, light reflected by the plane mirror is projected onto a plane that is along a mounting surface of the housing, and in the second projection mode, light from the concave mirror is projected onto a plane that is substantially orthogonal to the mounting surface of the housing without traveling through the plane mirror. 
 
     
     
       14. The image projection apparatus according to  claim 13 , further comprising a transparent flat plate, wherein the housing has an opening on an optical path connecting the concave mirror and the plane mirror, and the transparent flat plate is provided in the opening without leaving space. 
     
     
       15. An image projection apparatus, comprising:
 a projection optical system including one or more lenses, a concave mirror, and a planar optical substrate that are provided in order from a light incidence side on which incident light is incident, and configured to project an image using the incident light, 
 wherein the one or more lenses are configured to form an intermediate-focused image on a near side of the concave mirror, the planar optical substrate is configured to reflect a part of the incident light while allowing the other part of the incident light to transmit therethrough, and the light having transmitted through the planar optical substrate is projected onto a second surface intersecting with a first surface; and 
 a transparent flat plate on an optical path connecting the concave mirror and the plane mirror, 
 wherein the one or more lenses configure a symmetric optical system disposed on an optical axis, and 
 wherein a distance, at which each of a passing beam centroid position on the light incidence side of the transparent flat plate and a passing beam centroid position on a light emission side of the transparent flat plate are disposed from the optical axis of the one or more lenses, is based on a focal distance of the projection optical system. 
 
     
     
       16. An image projection method, comprising:
 reflecting, by a concave mirror, light having transmitted through one or more lenses after forming an intermediate-focused image of the light, 
 wherein the intermediate-focused image is formed by the one or more lenses on a near side of the concave mirror; and 
 projecting, using a projection optical system, an image onto a projection plane through reflecting the light reflected by the concave mirror by a plane mirror that has an aspect ratio of 1.9 or more, 
 wherein the concave mirror and the plane mirror are connected using a transparent flat plate on an optical path, 
 wherein the one or more lenses configure a symmetric optical system disposed on an optical axis, and 
 wherein a distance, at which each of a passing beam centroid position on a light incidence side of the transparent flat plate and a passing beam centroid position on a light emission side of the transparent flat plate are disposed from the optical axis of the one or more lenses, is based on a focal distance of the projection optical system. 
 
     
     
       17. An image projection method, comprising:
 reflecting, by a concave mirror, light having transmitted through one or more lenses after forming an intermediate-focused image of the light, 
 wherein the intermediate-focused image is formed by the one or more lenses on a near side of the concave mirror; and 
 projecting, using a projection optical system, an image through reflecting the reflection light reflected by the concave mirror by a plane mirror disposed on a passage of the reflection light and then through applying the light reflected by the plane mirror onto a projection plane, or projecting the image through applying the reflection light reflected by the concave mirror onto the projection plane without disposing the plane mirror on the passage of the reflection light, 
 wherein the concave mirror and the plane mirror are connected using a transparent flat plate on an optical path, 
 wherein the one or more lenses configure a symmetric optical system disposed on an optical axis, and 
 wherein a distance, at which each of a passing beam centroid position on a light incidence side of the transparent flat plate and a passing beam centroid position on a light emission side of the transparent flat plate are disposed from the optical axis of the one or more lenses, is based on a focal distance of the projection optical system.